1. Field of the Invention
This invention relates generally to silicon-containing films useful in the semiconductor industry, and more particularly to processes for making doped silicon and silicon alloy films using silicon-containing chemical precursors as sources for compound or doped films.
2. Description of the Related Art
Silicon and silicon-containing materials (e.g., silicon germanium, silicon germanium carbon, silicon carbon alloys, silicon carbide, etc.) are widely used in semiconductor films in integrated circuits with electronic band gap energies that are a function of their specific elemental composition. By incorporating dopant elements, primarily derived from the Group III and Group V families of elements, these semiconductors can be transformed into p-type (electron deficient) and n-type (electron rich) semiconductors. These doped materials are the building blocks for a number of microcircuit devices e.g., transistors.
There are three primary processes by which silicon-containing (xe2x80x9cSi-containingxe2x80x9d) materials are doped with electrically active atoms of the Group III and Group V families of elements: (1) ion implantation, (2) in situ doping during chemical vapor deposition, and (3) solid source diffusion. In ion implantation processes, a dopant precursor in a reaction chamber is fragmented to form a dopant ion and then mass-selected through the use of a magnetic field. These mass-selected species are then collimated into a beam of charged species with an incident energy determined by the extraction voltage of the process. Doping is accomplished by directing this beam onto the Si-containing material. Ion implantation of boron is typically accomplished using dopant precursors such as diborane (B2H6), boron trifluoride (BF3), isotopically enhanced 11B boron trifluoride and decaborane (B10H14). Typical dopant precursors for phosphorus and arsenic are phosphine (PH3) and arsine (AsH3), respectively.
In chemical vapor deposition (CVD) processes, the Si-containing material can be doped in situ by supplying the dopant precursor to the CVD chamber during the deposition of the Si-containing material. Typical dopant precursors for in situ doping of silicon-based materials include diborane, phosphine, and arsine.
In solid source diffusion applications, the atom(s) to be incorporated into the Si-containing material are either deposited in a relatively pure form on the surface of the material to be doped or are constituents of a heavily doped Si-containing film that is deposited on the surface of the material to be doped. The dopant atom(s) thus deposited are then diffused into the Si-containing material during a subsequent thermal anneal/drive process step. Typical dopant sources for the deposition of the dopant-containing overlayer include diborane, arsine, and phosphine. Examples of solid diffusion sources include heavily doped amorphous silicon and doped phosphorus-rich borophosphosilicate glass (BPSG).
The doping processes described above are employed widely within the industry for the manufacture of n-type and p-type silicon-based semiconductor materials. Each of these processes has limitations and drawbacks. For instance, the use of conventional dopant precursors often introduces unwanted elements. In the case of hydride dopant precursors, such as diborane and phosphine, various partially hydrogenated species formed during ion implantation create a xe2x80x9cmass envelopexe2x80x9d from which it is difficult to select the desired dopant species. This difficulty arises from the very small total mass of the fragments and the differences in mass between the various hydrogenated species (e.g., PH2+, PH+, P+, etc.), as well as the any overlap in mass between isotopes (e.g., boron has two stable isotopes with high natural abundancy, 11B and 10B). The use of hydride dopant precursors for in situ CVD and diffusion source doping often has drawbacks, including: (1) poor dopant incorporation at low film deposition temperature (particularly for arsenic), (2) segregation of dopant atoms along grain boundaries in polycrystalline silicon-based materials, (3) decreased deposition rate of polycrystalline materials as the concentration of in situ dopant precursors is increased, particularly at low temperature, (4) low percentage of electrically active dopant species relative to the total concentration of dopant atoms present within the silicon-based material, particularly for low deposition temperature, requiring separate activation steps that consume thermal budget, (5) poor control over the distribution of the dopant atoms following subsequent thermal processing to drive the dopant and form a p-n junction arising from multiple diffusion pathways available due to the partially incorporated nature of the dopant atoms (i.e., dopant atoms are substitutionally incorporated within the crystalline framework of the silicon-based material as well as incorporated along grain boundaries and/or the surface of the film), and/or (6) limitations on the total concentration of electrically activated dopant atoms that can be incorporated within the silicon-based material as a function of solid solubility, particularly at low deposition temperature.
The n-type dopant precursors or sources commonly utilized include phosphine and arsine. In addition to the problems cited above for the use of hydride dopant sources, halide sources entail other difficulties such as contamination of the silicon-based material with halide elements, particularly at low deposition temperature, and/or difficulty in delivering the dopant source to the reactor chamber as a function of precursor volatility. Many halides are low volatility liquids that require the use of a bubbler to deliver the precursor. This can also introduce problems with repeatability.
U.S. Pat. No. 4,910,153 concerns the fabrication of negatively-doped hydrogenated amorphous silicon alloys at relatively low deposition temperatures. Such hydrogenated amorphous silicon alloys generally contain 10 atomic % or more of hydrogen, which is desirable for certain photosensor applications. See U.S. Pat. No. 4,491,626 (cited in background section of U.S. Pat. No. 4,910,153). The use of trisilylarsine and trisilylphosphine as dopants is disclosed in U.S. Pat. No. 4,910,153, but that patent does not address the problems discussed above which are encountered when doping non-hydrogenated Si-containing materials or when doping crystalline Si-containing materials, such as polysilicon and epitaxial silicon. U.S. Pat. No. 4,200,666 concerns the deposition of hydrogenated silicon nitride using trisilylamine, but does not disclose methods for making non-hydrogenated Si-containing materials.
Thus, a number of problems remain with respect to making Si-containing films such as silicon alloys and doped amorphous silicon, polysilicon, and epitaxial silicon.
The inventors have discovered that doped Si-containing films can be made using chemical precursors that comprise at least one silicon atom and at least one Group III or Group V atom. In accordance with one aspect of the invention, a deposition process is provided for making a non-hydrogenated Si-containing film, comprising:
providing a vapor deposition chamber having a substrate disposed therein,
introducing a dopant precursor to the chamber, wherein the dopant precursor comprises at least one silicon atom and at least one Group III and/or Group V atom, and
depositing a non-hydrogenated Si-containing film onto the substrate.
Another aspect of the invention provides a deposition process for making an at least partially crystalline Si-containing film, comprising:
providing a chemical vapor deposition chamber having a substrate disposed therein,
introducing a silicon source and a dopant precursor to the chamber, wherein the dopant precursor is comprised of at least one silicon atom and at least one Group III and/or Group V atom, and
depositing a doped Si-containing film onto the substrate.
Another aspect of the invention provides a chemical vapor deposition process for making a Si-containing film, comprising:
providing a chemical vapor deposition chamber having a substrate disposed therein,
introducing a silicon source and a dopant precursor to the chamber, wherein the dopant precursor is comprised of at least one silicon atom and at least one Group III and/or Group V atom,
depositing a doped amorphous Si-containing film onto the substrate, and
heating the doped amorphous Si-containing film to a temperature in the range of about 550xc2x0 C. to about 700xc2x0 C. for a period of time effective to at least partially crystallize the doped amorphous Si-containing film.
Another aspect of the invention provides an ion implantation process for making a doped Si-containing film, comprising:
providing a Si-containing film on a substrate,
providing an ionization chamber upstream of the substrate,
introducing a dopant precursor to the ionization chamber, wherein the dopant precursor comprises at least one silicon atom and at least one Group III or Group V atom,
ionizing at least a portion of the dopant precursor to form dopant excited species by applying electromagnetic energy to the dopant precursor,
applying a magnetic field to the dopant excited species to create a sub-population of mass-selected dopant excited species, and
directing at least a portion of the sub-population of mass-selected dopant excited species onto the Si-containing film to produce a doped Si-containing film.
Another aspect of the invention provides a method for making a doped Si-containing film, comprising:
providing a Si-containing film,
forming a plasma from a gas comprising a dopant precursor selected from the group consisting of (H3Si)3-xMRx, (H3Si)3N, and (H3Si)4N2, wherein R is H or D, x=0, 1 or 2, and M is selected from the group consisting of B, P, As, and Sb; and
implanting active species of the dopant precursor from the plasma into the Si-containing film by ion implantation.
These and other aspects of the invention will be understood in view of the preferred embodiments described in more detail below.